Flip chip mounting is known as a method for mounting a semiconductor chip on a circuit substrate and the like. This is suitable for an apparatus that requires small size and/or thinness strongly. Furthermore, since this method allows heat of chip to transmit easily to a substrate, it is also used for mounting light-emitting diodes that may cause a problem of heat generation.
In the flip chip mounting, a chip is joined to a substrate via a protruding terminal called as a bump. Further, a structure in which a columnar metal is interposed between an electrode pad of a chip and a bump is also known (e.g. JP-A 2008-84920 (Kokai)). The columnar metal absorbs stress caused by a difference in coefficient of thermal expansion between the chip and the substrate; therefore, joining reliability can be enhanced.
The higher the aspect ratio (ratio of height to width) of the columnar metal is, the higher stress relaxation effects are. In order to increase the aspect ratio of the columnar metal, the columnar metal may be made thin or high. However, if the columnar metal is thin, concerns remain in regard to reduced joining strength due to the reduced area of joining to the bump. Furthermore, heightening the columnar metal increases plating cost for forming the columnar metal, and goes against the requirement of reducing thickness.